1. Field of the Invention
The present invention relates to a method for protective encapsulation of pipe loops installable on the seabed or one or more parts of pipes or pipelines, respectively, in the need of local protection against external loads, such as falling loads, trawl appliances drawn laterally across the pipe loop or the pipeline, as well as to counteract that sand and gravel mass beneath the pipe is being washed out, said pipe loop or other pipe being intended to convey oil and/or gas which can give rise to partly large temperature variations, and following expansion and contraction phenomena, and wherein the pipe loop or other pipe during the installation is lowered down from surface position, and wherein the pipe loop or other pipe in operative position of use on the seabed is surrounded by a protective cover which, preferably, in a final operation, is covered by a layer of chippings, or is kept in position in another, not specified way, e.g. by means of anchors.
Likewise, the invention relates to a device for protective encapsulation of a pipe loop or other pipe for the same general purpose, comprising a protective cover, possibly consisting of a number of joinable sections, jointly corresponding to the length of the pipe loop and shaped and designed in order to accommodate and surround a correspondingly long pipe portion.
Said protective cover or cover section, respectively, may have a closed, locally perforated, e.g. triangular cross-section with rounded corners and a flat floor-space/bottom wall to be placed against the seabed surface and which, internally, does not counteract the extensions and contractions of the pipe due to temperature alternations. Seabed-installed pipes and pipelines conveying gas and/or oil may vary to such a degree that the pipe will have to lengthen/shorten itself e.g. two metres at each end. A temperature of up to 110xc2x0 C. is an adequate example associated with oil and/or gas temperature when conveyed in pipes along the seabed.
2. Background
Pipe loops of this kind extend usually between underwater structures, but the protection method and device, respectively, according to the invention may as advantageously be used for pipe or local pipe sections of similar kind.
In such cases, in accordance with prior art technique, a pipe loop is first lowered down by means of a so called yoke, a kind of elongate boom insignificantly exceeding the shortest distance between the outer ends of the pipe loop, the pipe loop being attached to the boom, fixing means being fastened to the boom for the lowering operation. After the pipe loop""s lowering and positioning on the seabed, a protective cover is mounted around the pipe by means of divers and/or underwater vessels. Thereafter, a further vessel will provide covering of the pipe loop included within the protective cover, with chippings.
Known and conventional technique is very time-consuming and expensive.
The object of the invention has been, with simple and cheap means, to indicate a method and provide a device for protective encapsulation of a pipe loop or other pipe installable on the seabed, wherein the installation of the pipe, from the installation starts until the pipe rests on the seabed in protected condition, can be carried out in a considerable shorter time and with fewer vessels than before.
The object is achieved by proceeding in accordance with the characterizing clause of the first method claim. The first apparatus claim defines a suitable device for carrying out this method.
According to the invention, the protective cover is mounted on the pipe loop or other pipe in surface position, for, thereupon, to be lowered down to the installation place on the seabed from a surface vessel in at least partly protected condition.
This step involves that one can not only perform encapsulation of the pipe loop within the protective cover/jacket above water (on the place of production) instead of on the seabed and, thus, perform the necessary working operation on a far more convenient place where, moreover, the working conditions may be arranged optimally for the particular operations; besides this, the significant advantage is achieved that the required fasteners for the lowering-down wires from the surface vessel now may be provided on or attached to, respectively, the protective cover/jacket or the joined sections thereof, respectively. This results in that lowering of a pipe loop does not require the previously usual, very elongate yoke, and one is spared from releasing the pipe loop from the yoke at seabed level.
When the pipe loop thusly encapsulated within the protective cover has come into position on the seabed and each of its two ends has been coupled to a underwater structure belonging thereto, one can, if desired or necessary, place a layer of chippings on top of the protective cover with the pipe loop encapsulated therein. For example this can be desirable in fairway where bottom trawl fishing is usual. The layer of chippings will usually acquire the shape of an approximately triangular cross-section with a rounded top, and a bottom trawl will readily cross such a hindrance without getting entangled therein and without damaging or displacing the cover with the therein positioned, freely expanding/contracting pipe loop.
The protective cover surrounds the pipe with a clearance, and this clearance may, at least partly, advantageously be utilised for the filling of insulation material. Oil which becomes stationary within the pipe during a brief stoppage, will, thus, be insulated against cooling and solidification, so that these undesired states are delayed. Further heating may take place by installing heating pipes directly on the pipe loop.
In the cover or in one or more cover sections, respectively, in the bottom wall, through-going holes may be formed in order to, during the installation of cover/jacket with encapsulated pipe, be capable of letting seawater into the space between the outside of the pipe and said insulation""s inside.
Hoisting means in the form of fasteners on cover and, possibly, on pipe loop may consist of attachment armatures in steel and/or soft hoisting straps for wire. Fasteners on the pipe loop are, preferably, releasable, so that they can be removed when the pipe loop included within the protective cover has arrived into position on the seabed and the ends thereof each has been coupled to an underwater structure belonging thereto. Prior to such a coupling operation, cover and pipe loop are releasably attached to each other, so that pipe loop and cover become mounted in correct positions in relation to each other. Subsequently to the pipe loop""s interconnection between the structures, the connection between cover and pipe loop is released.